Deactivation of Red Mud by Primary Aluminum Production Wastes

Current global environmental challenges and, above all, global warming associated with a change in the carbon balance in the atmosphere has led to the need for urgent and rapid search for ways to reduce greenhouse gas emissions into the atmosphere, which primarily include carbon dioxide as a by-product of human activity and technological progress. One of these ways is the creation of industries with a complete cycle of turnover of carbon dioxide. Aluminum is the most sought-after nonferrous metal in the world, but its production is not environmentally safe, so it constantly requires the development of knowledge-intensive technologies to improve the technological process of cleaning and disposal of production waste, primarily harmful emissions into the atmosphere. Another environmental problem related to aluminum production is the formation and accumulation in mud lagoon of huge amounts of so-called highly alkaline "red mud," which is a waste product of natural bauxite raw material processing into alumina - the feedstock for aluminum production. Commonly known resources and technological methods of neutralizing red mud and working with it as ore materials for further extraction of useful components are still not used because of their low productivity and cost-effectiveness. This article describes the negative impact of waste in the form of "red" mud and carbon dioxide of primary aluminum production on the environment. The results showed that thanks to carbonization of red mud using carbon dioxide, it is possible to achieve rapid curing and its compact formation for safer transportation and storage until further use. Strength tests of concrete samples filled with deactivated red mud were also carried out, which showed the prospects of using concrete with magnesia binder.

Hydrometallurgical processing of technogenic finely dispersed fluorocarbon-containing raw materials of primary aluminum production

The purpose of the paper is to determine the conditions for the maximum transition of fluorine from the technogenic raw materials of primary aluminum production (mature sludge) into solution under alkaline leaching. The object of research is the mature sludge, which is formed from technogenic finely dispersed materials of aluminum production in the baths with Soderberg anodes (tailings of coal foam flotation, gas cleaning sludge, electrostatic precipitator dust) and stored close to the enterprise. Analytical studies of the initial sample and leaching products have been carried out according to the certified methods using chemical, X-ray phase and titrimetric analysis methods. It is shown that, the main percentage of the three sludge components belongs to the dust of electrostatic precipitators (~ 79.7%) and coal foam flotation tailings (~ 15.8%). It has been determined that the gas cleaning sludge features the richest composition of useful components (in the sum of F, Na and Al ~ 63%). According to the data of X-ray phase analysis, the sludge sample from the sludge storage mainly contains cryolite (up to 78.7%), carbon (11.9%), calcium-magnesium carbonate from the dolomite series (4.44%), and trace amounts of corundum and fluorite. The results of the conducted experiments on fluorine leaching from the sludge sample by the caustic soda solution allow to estimate the main process parameters: temperature - 75–80°С, duration - 60 min, NaOH concentration - 3.0% (with the W:T ratio of 10:1 and a stirrer speed of ~ 1005– 1010 rpm). According to the analytical data on the chemical composition of leaching cake, the fluorine content in the solid phase reduces by 88.1%. The experiments carried out on alkaline leaching of fluorine from the sample of mature sludge formed under primary aluminum production by the electrolysis of cryolite-alumina melts in the baths with self-baking anodes allowed to find out that the maximum decrease of fluorine content in the sample is achieved under the conditions of maintaining the process parameters including temperature, duration, reagent concentration in optimal modes.

REGULATION OF THE TEMPERATURE REGIME FOR CASTING CARBON AND HIGH-MANGANESE STEEL

The possibility of using insulating slag-forming mixtures based on highly dispersed carbon-containing material (VUM), which is a waste product of primary aluminum production, to reduce heat loss was considered.

The Adsorption Behavior of Moisture on Smelter Grade Alumina during Transportation and Storage—for Primary Aluminum Production

Smelter grade alumina (SGA) plays multiple roles in the Hall–Héroult process for primary aluminum production. Given its very porous nature, one major role of SGA is to adsorb toxic hydrogen fluoride (HF) in the dry scrubber. However, also because of its porous nature, SGA inevitably adsorbs ambient moisture. This paper discusses the influence of alumina properties, including pore size distribution and specific surface area, on the physical adsorption of water vapor on SGA, as well as the adsorption kinetics. The result shows that the adsorption enthalpy of moisture on SGA is in the range of 4–13 kJ/mol. The adsorption capacity increases significantly with the particle specific surface area and total pore volume. A higher adsorption temperature indicates a much faster adsorption rate but corresponds to a lower equilibrium adsorption capacity.

Soft Sensors in the Primary Aluminum Production Process Based on Neural Networks Using Clustering Methods

Primary aluminum production is an uninterrupted and complex process that must operate in a closed loop, hindering possibilities for experiments to improve production. In this sense, it is important to have ways to simulate this process computationally without acting directly on the plant, since such direct intervention could be dangerous, expensive, and time-consuming. This problem is addressed in this paper by combining real data, the artificial neural network technique, and clustering methods to create soft sensors to estimate the temperature, the aluminum fluoride percentage in the electrolytic bath, and the level of metal of aluminum reduction cells (pots). An innovative strategy is used to split the entire dataset by section and lifespan of pots with automatic clustering for soft sensors. The soft sensors created by this methodology have small estimation mean squared error with high generalization power. Results demonstrate the effectiveness and feasibility of the proposed approach to soft sensors in the aluminum industry that may improve process control and save resources.

Recycling of Aluminum

Aluminum is the second most used metal in the world because of its properties including good corrosion resistance, low density, high electrical conductivity and good thermal conductivity. However, the negative environmental impact from production of primary aluminum is due to the corresponding impact of red mud and release of fluorides which is devastating to forests and the space required for waste disposal. Recycling, in addition to reducing the impact of disposal of the by-products of primary aluminum production also consumes a great amount of electricity. Therefore, recycling of aluminum scrap is of increasing interest. In this article, the following factors involved in aluminum recycling are discussed: environmental and energy impact, secondary metallurgy of aluminum, fundamentals of aluminum recovery using salt flux, recovery of aluminum drosses by milling and preliminary treatments of scrap.